(a) Field of the Invention
The present invention relates to a system for controlling a motor of a vehicle. More particularly, the present invention relates to a system for controlling a motor of a vehicle that improves fuel economy by minimizing a sum of heat generated by the motor and heat generated by a converter.
(b) Description of the Related Art
Recently, environmentally-friendly vehicles such as hybrid vehicles and electric vehicles have attracted increasing attention due to energy depletion and environmental pollution. The environmentally-friendly vehicles typically include a motor that generates a driving torque by using electricity from a battery, and a permanent magnet synchronous motor is mainly used as the motor.
A permanent magnet synchronous motor (PMSM) has high power/high efficiency characteristics and is widely used in industrial applications. The PMSM has broadened its use to a drive motor of the environmentally-friendly vehicle.
Because an engine can be controlled regardless of the amount fuel amount remaining in a fuel tank (gasoline and diesel engines widely used as driving devices of conventional vehicles), the fuel amount remaining in the fuel tank does not operate directly as a control variable for controlling the engine. In addition, because a permanent magnet synchronous motor using commercial electricity as an input power uses the commercial electricity supplied from a sub-station, an input voltage is very stable. Therefore, a change in the input voltage does not affect control of a controller and speed or torque of the permanent magnet synchronous motor greatly when driving the permanent magnet synchronous motor.
However, the permanent magnet synchronous motors receive input voltage mainly from a power supplying device (e.g., battery) mounted in the vehicle. Because the power supplying device mounted in the vehicle has a limited size and capacity, an output voltage changes according to charging state thereof. Accordingly, the charging state of the power supplying device affects a controller of the permanent magnet synchronous motor directly, and changes control state of the motor as a result. Change in the input voltage applied to the controller directly affects current and voltage applied to an inverting module in an inverter and an electric coil of the permanent magnet synchronous motor, and thereby changes heat generation in accordance therewith. Therefore, heat that is greater than the required heat generation may be generated in the permanent magnet synchronous motor.
An increase in heat generated at the motor and the controller in the vehicle using the permanent magnet synchronous motor as power source works on cooling burden and causes the fuel economy of the vehicle to be reduced. Therefore, it is very important to minimize heat generation in a motor control system.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.